Why would there be a sewer gas smell in the basement landing whenever the downstairs toilet which backs up to landing the is flushed?

Answer 1

If there's a basement floor drain close by, sometimes the all the water can evaporate out of the trap. This can allow sewer smells into the house. Just run some water thruough the floor drain to fill the trap back up. Ditto for any drain that doesn't get used very often. More input from FAQ Farmers: * Maybe the vent in the wall isn't connected properly or came apart. I would think you'd have a sewer smell all the time but maybe it just gets bad enough when things get stirred up to notice. * Vent pipes are a major source of sewer odors. Vent pipe filters eliminate these odors while removing greenhouse gases. Used zeocarbon is then put back into the soil.